them once.
- solidify/matrix.h, solidify/matrix.c: 2D matrix operations
- solidify/Makefile (OBJS): added matrix.o
- solidify/face.h (struct matrix): moved to solidify/matrix.h
- solidify/overlap.c (point, merge_matrix, draw_map): precalculate a single
vA+b transformation instead of stepwise transforming the vector inside
the loop
- solidify/overlap.c (do_shift): now that the math is right (or at least
better), reverse the shift
